The flyback power module employs a transformer for power delivery from the primary side to the secondary side. For output feedback from the secondary side to regulate the output voltage, the secondary side requires a voltage sensor, typically including a shunt regulator and an optical coupler. However, these devices increase the size and the costs of the power module.
For smaller size and lower costs, some flyback power modules, for example, U.S. Pat. Nos. 5,438,499, 6,480,399, 6,721,192, 6,781,357, 6,833,692, 6,862,194, 6,967,472 and 6,977,824, extract output information from the primary side for stable output voltage. However, such primary feedback flyback power modules lack of secondary side information, and thus will have output offset in different environment which include resistance error or transformer or power supply even different diode. For primary flyback controller, because there is no secondary side information, the accuracy depends on strict transformer and secondary side component production control. This is a big issue for cost and mass-production quality control.